Scrubbers are air pollution control devices, used to remove particulates and/or gases from industrial exhaust streams. In a wet scrubber, the exhaust stream contacts a liquid which absorbs the pollutant, and leaves the device clean from the pollutants, or at least, cleaner than it enters.
U.S. Pat. No. 5,354,363, the disclosure of which is incorporated herein by reference, describes a wet scrubber, which employs liquid gallium to absorb vapor phase mercury from a hot gas exhaust stream in an industrial exhaust system. The temperature of the liquid gallium is elevated for optimum adsorption efficiency, and subsequently lowered to separate the absorbed mercury.
U.S. Pat. No. 6,855,859, the disclosure of which is incorporated herein by reference, describes a wet scrubber for removing elemental and oxidized mercury from a gas. The scrubber utilizes two aqueous solutions, each being contacted with the gas at a different location in the scrubber. A first aqueous solution is used to oxidize the elemental mercury to obtain a chloride salt, and the second—to react the chloride salt with a sulfide to obtain insoluble mercuric sulfide. The mercuric sulfide precipitates, and the gas leaves the solution with less elemental mercury.
US 2007/0123660 to deGouvea-Pinto, the disclosure of which is incorporated herein by reference, describes the use of an ionic-liquid/ligand combination, immobilized on a silica substrate, for separating mercuric chloride from nitrogen.
deGouvea-Pinto states that “the ionic liquid is a chemically active environment for solubilization or reaction with the metal vapor. For example, oxidized metals can be made to absorb with high affinity for subsequent chelation, and elemental metals can be oxidized by the layer [of ionic liquid] prior to adsorption on the ligand. [ . . . ] It has been demonstrated that elemental mercury is captured in this ionic liquid [=pyrrolidinium bis(trifluoromethane sulfonyl)imide salt] due to simultaneous oxidation and solvation. Furthermore, the use of additives to further enhance the reactive environment in the ionic liquid has also been demonstrated. For example, KMnO4 (up to 0.25 mmole) has been used as an additive to enhance the oxidation of elemental mercury”.
deGouvea-Pinto also states that “a wide variety of combinations of ionic liquids, chelating agent, or other ligands, and solid supports can be used together, as well as the ionic liquid/ligand combination independent of a solid substrate will function to adsorb/absorb metal atoms in a gaseous stream”.
Other publications of deGouvea-Pinto relating to capture of mercury by ionic liquids include:
Mercury extraction by ionic liquids: temperature and alkyl chain length effect Tetrahedron Letters 48 (2007) 1767-1769;
Pyrrolidiniiom Imides: Promising Ionic Liquids for Direct Capture of Elemental Mercury from Flue Gas Water Air Soil Pollut: Focus 8 (2008) 349-358; and
Room Temperature Ionic Liquids for Mercury Capture from Flue Gas Ind. Eng. Chem. Res. Published on the web Oct. 1, 2008.
It is noted that citation or identification of any reference in this application in general and in the background section in particular, shall not be construed as an admission that such reference is available as prior art to the present invention.